Abstract
Treating extensively drug-resistant (XDR) tuberculosis (TB) is a serious challenge. Culture-based drug susceptibility testing (DST) may take 4 weeks or longer from specimen collection to the availability of results. We developed a pyrosequencing (PSQ) assay including eight subassays for the rapid identification of Mycobacterium tuberculosis complex (MTBC) and concurrent detection of mutations associated with resistance to drugs defining XDR TB. The entire procedure, from DNA extraction to the availability of results, was accomplished within 6 h. The assay was validated for testing clinical isolates and clinical specimens, which improves the turnaround time for molecular DST and maximizes the benefit of using molecular testing. A total of 130 clinical isolates and 129 clinical specimens were studied. The correlations between the PSQ results and the phenotypic DST results were 94.3% for isoniazid, 98.7% for rifampin, 97.6% for quinolones (ofloxacin, levofloxacin, or moxifloxacin), 99.2% for amikacin, 99.2% for capreomycin, and 96.4% for kanamycin. For testing clinical specimens, the PSQ assay yielded a 98.4% sensitivity for detecting MTBC and a 95.8% sensitivity for generating complete sequencing results from all subassays. The PSQ assay was able to rapidly and accurately detect drug resistance mutations with the sequence information provided, which allows further study of the association of drug resistance or susceptibility with each mutation and the accumulation of such knowledge for future interpretation of results. Thus, reporting of false resistance for mutations known not to confer resistance can be prevented, which is a significant benefit of the assay over existing molecular diagnostic methods endorsed by the World Health Organization.